(1) Field of the Invention:
This invention relates to a metal-made carrier body for an exhaust gas cleaning catalyst which is generally interposed as an exhaust gas cleaning means at an intermediary point in an exhaust gas system of an automotive vehicle. More specifically, this invention is concerned with a metal-made carrier body for an exhaust gas cleaning catalyst, which can improve the efficiency of contact between an exhaust gas and a catalyst layer to enhance the cleaning efficiency of the exhaust gas.
(2) Description of the Related Art:
As metal-made carrier bodies for carrying an exhaust gas cleaning catalyst, there have conventionally been known those obtained by rolling at least one planar metal band and at least one corrugated metal band, each of said bands being made of a thin metal sheet, together into a spiral form with a view toward increasing the carrying area per unit volume, in other words, increasing the effective contact area between an exhaust gas and an exhaust gas cleaning catalyst as much as possible and further with a view toward reducing the weight of the metal-made carrier body as much as feasible. For example, a planar band of a heat-resistant thin iron-chromium steel sheet of 0.1 mm thick or less and a corrugated band obtained by forming into a corrugated configuration a thin steel sheet of the same type as that mentioned above are superposed one over the other to establish contacts therebetween. They are then rolled together into a spiral form, thereby providing a multi-layered composite body defining many network-patterned gas flow passages along the central axis thereof. The thus-rolled multi-layered composite body is enclosed in a metal casing which is open at both ends thereof. The contacts between the planar band and corrugated band and contacts between these bands and the metal casing are bonded by welding, brazing or the like.
As has been described above, a metal-made carrier body for supporting an exhaust gas cleaning catalyst thereon is fabricated by rolling a planar metal band and a corrugated metal band, each of said bands being made of a thin metal sheet, together into a spiral form. In its fabrication process, the rolling is effected using a metal-made mandrel of, for example, about 3-6 mm in diameter as a core and the mandrel is thereafter extracted.
Accordingly, the multi-layered spiral composite body of the planar metal band and corrugated metal band always defines a central and axial bore corresponding to the mandrel in view of its fabrication process.
When an exhaust gas cleaning catalyst such as platinum, palladium or rhodium is carried on the metal-made carrier body having such a central and axial bore in its rolled multi-layered composite body and is then used as a catalytic converter, a portion of an exhaust gas is allowed to pass through the central and axial bore so that the cleaning performance is reduced to a significant extent.